1. Field of the Invention
The present invention relates to a method for the production of heat exchangers of the type including a fin block made of porous metal having a multiplicity of continuous pores through which one of the fluids to be heat-exchanged flows. The heat exchangers produced by the method of the invention are used for causing heat-exchange between two fluids of different temperatures, and have many applications. For example, the heat exchangers may be used as heat exchangers for fan-coil unit and as evaporators and condensers for refrigerating devices and air conditioning systems in which air is used as one of the fluids to be heat-exchanged.
2. Description of the Prior Art
The prior art having relevance to the present invention includes a heat exchanger disclosed in Laid-Open Japanese Patent Application, Laid-Open No. 154853/75 which comprises a fin block formed of foamed metal body produced by adding a foam-producing agent into molten metal to thereby cause foaming of the molten metal. Also known in the art is a heat exchanger disclosed in Laid-Open Japanese Patent Application, Laid-Open No. 23848/76 which uses a metal fin block produced by bonding together metal particles for example by sintering process. However, the former Japanese Application has the disadvantage that flow resistance imposed on the fluid passing through passages formed by the pores is increased, since very thin interconnecting portions between the continuous pores are constricted and independent and since discontinuous pores tend to be produced in the metal fin block. Further, it is difficult to obtain the foamed metal fin block having uniform density over the entire area.
In the latter Japanese Application, gaps between the metal particles provide passages for fluid. With this structure, it is difficult to obtain high percentage of gap area in the produced metal fin block. Further, this prior art heat exchanger suffers from high production time as well as high price.
Because of the problems encountered with the prior art heat exchangers described above, they have not been practically used in the field.
Nowadays, it is a common practice to use heat exchangers including plate-like fins. The majority of the heat exchangers now commonly used are heat exchangers of the cross-fin type in which a large number of plate-like fins are secured to the heat-transmitting piping perpendicularly to its longitudinal axis in closely adjacent relation, to maximize the heat-transfer area.
Regardless of whether the heat-transmitting piping consists of a serpentine pipe or a plurality of parallel pipes interconnected by means of a header, the pipes must be connected together after the fins are secured thereto in a multiplicity of rows. Fabrication of a heat exchanger thus involves many process steps to be performed including assembling of the parts which is troublesome; and productivity is low because these process steps take a long time to perform. In heat exchangers of the cross-fin type, fluid flows through the gaps between the plate fins. Thus, it is impossible to increase the heat-transfer area by narrowing the gaps and increasing the number of fins, because such attempt will entail an increase in the resistance imposed on the flow of fluid and restrictions will be placed on the working of the pipes and fins.